Filter device

ABSTRACT

A filter device having desired characteristics is easily designed. The filter device includes a post-wall waveguide functioning as a resonator group including five congruent resonators (R 1  to R 5 ). The resonators (R 1 , R 2 ) include therein respective control posts (CP 1 , CP 2 ), and a shortest distance (d i ) from the control post (CP i ) to a narrow wall of the resonator (R i ) satisfies d 1 &gt;d 2 . The resonators (R 4 , R 5 ) include therein respective control posts (CP 4 , CP 5 ), and a shortest distance (d j ) from the control post (CP j ) to a narrow wall of the resonator (R j ) satisfies d 4 &lt;d 5 .

TECHNICAL FIELD

The present invention relates to a resonator-coupled filter device.

BACKGROUND ART

Band-pass filter devices designed for use in microwave andmillimeter-wave bands are disclosed in, for example, PatentLiterature 1. The band-pass filter devices are an aspect of a filterdevice.

These filter devices are provided by utilizing a post-wall waveguide(PWW) technique. Specifically, these filter devices are produced byusing a dielectric substrate which is sandwiched between a pair ofconductor layers. The substrate includes therein a plurality ofresonators which are coupled together. The plurality of resonators eachinclude: a pair of broad walls which is the pair of conductor layers;and a narrow wall which is a post wall composed of a plurality ofconductor posts which are arranged in a fence-like manner.

The post wall partitioning any two adjacent ones of the plurality ofresonators has a portion in which the conductor posts are absent so thata coupling window is provided. The two adjacent resonators areelectromagnetically coupled together via the coupling window. Somefilter devices can be composed of a first-stage resonator which isprovided with an input port and a last-stage resonator which is providedwith an output port, and other filter devices can be composed of thefirst-stage resonator, the last-stage resonator, and one or moreresonators provided between the first-stage and last-stage resonators.Thus, such a filter device in which a PWW is used is a resonator-coupledfilter device.

The filter device disclosed in FIG. 1 and FIG. 4 of Patent Literature 1is a five-pole filter device composed of five (five-stage) resonators.All of the resonators of the filter device are cylindrical. In addition,the five-stage resonators are disposed in a loop shape such that thefirst-stage resonator and the last-stage resonator are adjacent to eachother. The filter device further includes a control post which is madeof a conductor and is disposed on or near a side wall of each of theresonators. A change in position of the control post makes it possibleto change a resonance frequency of a corresponding resonator withoutchanging a basic design of the filter device.

Main design parameters of such a resonator-coupled filter device include(i) respective areas of the resonators seen in plan view and (ii) acoefficient of coupling between the resonators (i.e., the size of acoupling window). This is because the resonance frequency of each of theresonators (i.e., a center frequency in a passband of a filter device)depends on the area of a corresponding resonator, and the bandwidth ofthe passband depends on the coefficient of coupling between theresonators.

CITATION LIST Patent Literature Patent Literature 1

-   Japanese Patent Publication No. 6312910

SUMMARY OF INVENTION Technical Problem

The resonator-coupled filter device as described above has variouscoefficients of coupling between the resonators, i.e., various sizes ofcoupling windows, in order to obtain desired transmissioncharacteristics.

For example, for a resonator-coupled filter device which includes fiveresonators R₁ to R₅ and in which the first-stage resonator R₁ is coupledto an input waveguide R₈ and the fifth-stage resonator R₅ is coupled toan output waveguide R₉, the respective sizes of coupling windowsdecrease in the following order: (1) a coupling window coupling theinput waveguide R₅ and the resonator R₁ and a coupling window couplingthe resonator R₅ and the output waveguide R₉, (2) a coupling windowcoupling the resonator R₁ and the resonator R₂ and a coupling windowcoupling the resonator R₄ and the resonator R₅, (3) a coupling windowcoupling the resonator R₂ and the resonator R₃ and a coupling windowcoupling the resonator R₃ and the resonator R₄.

The sizes of the coupling windows influence resonance frequencies, whichare determined in accordance with respective effective areas of theresonators R₁ to R₅ in plan view, and change the effective areas fromrespective design values for areas of the resonators. Specifically, acoupling window which has a larger size causes a resonator to have aneffective area larger than the design value for the area of theresonator. Therefore, assuming that the resonators R₁ to R₅ share witheach other the same design value for the areas of the resonators, theeffective areas decrease in the following order: (1) the resonators R₁and R₅, (2) the resonators R₂ and R₄, (3) the resonator R₃.

In order to bring the respective effective areas of the resonators R₁ toR₅ closer to uniformity, it is necessary to make the design values forthe respective areas of the resonators R₁ to R₅ different among (1) theresonators R₁ and R₅, (2) the resonators R₂ and R₄, and (3) theresonator R₃. In addition, causing the resonators R₁ to R₅ to haverespective different areas affects the sizes of the coupling windows.This makes it necessary to redesign the respective sizes of the couplingwindows. Such a process for designing the filter device is complicatedbecause (i) the areas of the resonators R₁ to R₅ and (ii) the sizes ofthe coupling windows are required to be optimized while (i) and (ii) aremutually dependent.

A filter device in accordance with the present invention has been madein view of the above problems, and has an object to provide a filterdevice which can be designed by a simple design process.

Solution to Problem

In order to attain the object, a filter device in accordance with afirst aspect of the present invention includes a post-wall waveguidefunctioning as a resonator group including n resonators R₁, R₂, . . . ,R_(n) (n is an odd number not less than five) which areelectromagnetically coupled together and which are congruent with eachother. The resonators R₁, R₂, . . . , R_((n−1)/2) are configured suchthat (1) each resonator R_(i) (i=1, 2, . . . , (n−1)/2) includes thereina control post CP_(i) and (2) a shortest distance d_(i) from the controlpost CP_(i) to a narrow wall of the resonator R_(i) satisfies d₁>d₂> . .. >d_((n−1)/2). The resonators R_((n+1)/2+1), R_((n+1)/2+2), . . . ,R_(n) are configured such that (1) each resonator R_(j) (j=(n+1)/2+1,(n+1)/2+2, . . . , n) includes therein a control post CP_(j) and (2) ashortest distance d_(j) from the control post CP_(j) to a narrow wall ofthe resonator R_(j) satisfies d_((n+1)/2+1)<d_((n+1)/2+2)< . . . <d_(n).

Advantageous Effects of Invention

It is possible to design a filter device in accordance with an aspect ofthe present invention by a design process simpler than conventionaldesign processes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a filter device in accordance with a firstembodiment of the present invention, in which (a) of FIG. 1 is aperspective view of the filter device and (b) of FIG. 1 is a plan viewof a post-wall waveguide of the filter device illustrated in (a).

FIG. 2 is a view illustrating first and second variations of thepost-wall waveguide illustrated in FIG. 1 , in which (a) of FIG. 2 is aplan view schematically illustrating the first variation and (b) of FIG.2 is a plan view schematically illustrating the second variation.

FIG. 3 is a view illustrating third, fourth, and fifth variations of thepost-wall waveguide illustrated in FIG. 1 , in which (a) of FIG. 3 is aplan view schematically illustrating the third variation, (b) of FIG. 3is a plan view schematically illustrating the fourth variation, and (c)of FIG. 3 is a plan view schematically illustrating the fifth variation.

FIG. 4 is a view illustrating graphs, in which (a) of FIG. 4 is a graphillustrating characteristics of Example of the post-wall waveguideillustrated in FIG. 1 and (b) of FIG. 4 is an enlarged graphillustrating a portion of (a) of FIG. 4 .

DESCRIPTION OF EMBODIMENTS First Embodiment

(Structure of Filter Device)

The following description will discuss, with reference to FIG. 1 , astructure of a filter device 1 in accordance with a first embodiment ofthe present invention. (a) of FIG. 1 is a perspective view of the filterdevice 1. (b) of FIG. 1 is a plan view of a post-wall waveguide 11 ofthe filter device 1.

The filter device 1 includes the post-wall waveguide 11 which functionsas a plurality of (n: n is any integer not less than 2) resonators R₁ toR_(n) which are electromagnetically coupled together. The description ofthe first embodiment will discuss the case of n=5. In other words, thepost-wall waveguide 11 functions as five resonators R₁ to R₅. Theresonator R₂ is an example of a resonator R_((n−1)/2) recited in theclaims, the resonator R₃ is an example of a resonator R_((n+1)/2)recited in the claims, the resonator R₄ is an example of a resonatorR_((n+1)/2+1) recited in the claims, and the resonator R₅ is an exampleof a resonator R_((n+1)/2+2) recited in the claims. The resonators R₁ toR₅ which do not need to be particularly discriminated from each otherare each hereinafter referred to as a resonator R_(x).

The post-wall waveguide 11 includes a dielectric substrate 111, a firstbroad wall 112 provided on a first main surface (an upper surface inFIG. 1 and FIG. 2 ) of the dielectric substrate 111, a second broad wall113 provided on a second main surface (a lower surface in FIG. 1 andFIG. 2 ) of the dielectric substrate 111, and a post wall 114 providedinside the dielectric substrate 111.

The dielectric substrate 111 is a plate-like member made of a dielectricmaterial. The first embodiment employs quartz glass as the dielectricmaterial of which the dielectric substrate 111 is made. In this case,the dielectric substrate 111 can have a thickness of, for example, 860μm.

The first broad wall 112 and the second broad wall 113 are layered(filmy) members which are made of a conductor material. The firstembodiment employs copper as the conductor material of which the firstbroad wall 112 and the second broad wall 113 are made.

The post wall 114 is a collection of conductor posts which short-circuitthe first broad wall 112 and the second broad wall 113 and which arearranged in a fence-like manner, and serves as a narrow wall of thepost-wall waveguide 11. The conductor posts constituting the post wall114 are disposed at intervals sufficiently shorter than a wavelength ofan electromagnetic wave received by the post-wall waveguide 11. Thus,the post wall 114 serves as a conductor wall for the electromagneticwaves. The conductor posts can have a diameter of, for example, 100 μm,and an interval between the central axes of adjacent conductor posts canbe set to, for example, 200 μm. In the first embodiment, the conductorposts constituting the post wall 114 are each produced by forming aconductor layer on the inner wall of a through-hole passing through thedielectric substrate 111 or by filling the through-hole with aconductor. A pattern in which the post wall 114 is disposed isdetermined so that a space bounded by the first broad wall 112, thesecond broad wall 113, and the post wall 114 functions as the pluralityof resonators R₁ to R₅ which are electromagnetically coupled together.The pattern in which the post wall 114 is disposed will be describedlater with reference to another drawing.

The first embodiment employs quartz glass as the dielectric material ofwhich the dielectric substrate 111 of the post-wall waveguide 11 ismade. However, an aspect of the present invention is not limited tothis. The dielectric material of which the dielectric substrate 111 ofthe post-wall waveguide 11 is made can be any dielectric materialdifferent from quartz, such as, sapphire or alumina.

The first embodiment employs copper as the conductor material of whichthe first broad wall 112 and the second broad wall 113 of the post-wallwaveguide 11 are made. However, an aspect of the present invention isnot limited to this. The conductor material of which the first broadwall 112 and the second broad wall 113 of the post-wall waveguide 11 aremade can be any conductor material different from copper, such asaluminum or an alloy composed of a plurality of metallic elements.

Each resonator R_(x) is cylindrical in the first embodiment. However, anaspect of the present invention is not limited to this. The resonatorR_(x) can have the shape of, for example, a prism whose cross section(cross section parallel to the main surfaces of the dielectric substrate111) is a regular polygon which has at least six vertexes. When theresonator Rx is cylindrical, a circumscribed circle of the resonator Rxin plan view coincides with the outer edge of the broad walls of theresonator Rx. This makes it possible to use either the radius of theresonator Rx or the radius of the circumscribed circle of the resonatorRx to define a center-to-center distance between any two adjacent onesof the resonators. When the resonator Rx has a cross section which isnot a circle but a regular polygon that has at least six vertexes, it ispossible to use the radius of the circumscribed circle of the resonatorRx to define the center-to-center distance.

The number n of the resonators R₁ to R_(n) is five in the firstembodiment. However, an aspect of the present invention is not limitedto this. Specifically, the number n can be any number not less than two.The number n, which is an odd number in the first embodiment, can be aneven number as described later.

(Pattern in which post wall is disposed)

The following description will discuss, with reference to (b) of FIG. 1, the pattern in which the post wall 114 is disposed in the post-wallwaveguide 11. (b) of FIG. 1 is a plan view of the post-wall waveguide11. In (b) of FIG. 1 , the post wall 114 is illustrated, with a dottedline, as an imaginary conductor wall. The dotted line is obtained byconnecting, by arcs or straight lines, the respective centers of theconductor posts constituting the post wall 114.

The pattern in which the post wall 114 is disposed is determined so thata space bounded by the first broad wall 112, the second broad wall 113,and the post wall 114 includes the components below.

-   -   the input waveguide R₈,    -   the resonator R₁ electromagnetically coupled to the input        waveguide R₈ via a coupling window A81,    -   the resonator R₂ electromagnetically coupled to the resonator R₁        via a coupling window A12,    -   the resonator R₃ electromagnetically coupled to the resonator R₂        via a coupling window A23,    -   the resonator R₄ electromagnetically coupled to the resonator R₃        via a coupling window A34,    -   the resonator R₅ electromagnetically coupled to the resonator R₄        via a coupling window A45, and    -   the output waveguide R₉ electromagnetically coupled to the        resonator R₅ via a coupling window A59.

Since n=5 in the first embodiment, it is determined that i, j, and(n+1)/2 each recited in the claims are i=1, 2, j=4, 5, and (n+1)/2=3,respectively. The resonator R₁ and the resonator R₅ are examples of afirst-stage resonator and a last-stage resonator, respectively, eachrecited in the claims.

The resonators R₁ to R₅ are cylindrical and congruent with each other.In other words, the resonators R₁ to R₅ have respective radii r₁ to r₅each of which is a radius r_(a), which is shared among the resonators R₁to R₅. The input waveguide R₈ and the output waveguide R₉ have the shapeof a rectangular parallelepiped. The center-to-center distance betweentwo adjacent resonators (for example, the resonator R₂ and the resonatorR₃) is smaller than the sum of the radii of the two resonators. Forexample, a center-to-center distance D23 between the two adjacentresonators R₂ and R₃ satisfies D23<r₂+r₃ (=2r_(a)). This causes the twoadjacent resonators to be electromagnetically coupled to each other viaa coupling window. For example, the two adjacent resonators R₂ and R₃are electromagnetically coupled to each other via the coupling windowA23.

Two adjacent resonators are symmetric with respect to a plane containingthe central axes of the two resonators. For example, the two adjacentresonators R₂ and R₃ are symmetric with respect to a plane S23 (see (b)of FIG. 1 ) containing the central axes of the two resonators R₂ and R₃.In addition, the resonator group composed of the resonators R₁ to R₅ issymmetric with respect to a particular plane S (see (b) of FIG. 1 )which is orthogonal to the first broad wall 112. It is possible toeasily design the filter device 1 by giving such symmetries to the postwall 114 so as to reduce independent parameters which define the patternin which the post wall 114 is disposed.

Further, the resonator R₁ coupled to the input waveguide R₈ and theresonator R₅ coupled to the output waveguide R₉ are disposed so as to beadjacent to each other. Thus, the resonators R₁ to R₅ as a whole arearranged so as to have a loop shape. Such an arrangement enables thedielectric substrate 111 in which the post wall 114 is provided to bemore compact. This allows the dielectric substrate 111 to have a smallermagnitude of thermal expansion or thermal contraction which may becaused when an ambient temperature changes. It is therefore possible toreduce a change in characteristics of the filter device 1 which may becaused by the thermal expansion or contraction of the dielectricsubstrate 111 when the ambient temperature changes.

In the first embodiment, a waveguide coupled to the resonator R₁ is theinput waveguide R₈, and a waveguide coupled to the resonator R₅ is theoutput waveguide R₉. However, an aspect of the present invention is notlimited to this. Alternatively, the waveguide coupled to the resonatorR₁ can be the output waveguide, and the waveguide coupled to theresonator R₅ can be an input waveguide.

(Control Post)

As illustrated in (a) and (b) of FIG. 1 , the resonator R₁ includestherein a control post CP₁, the resonator R₂ includes therein a controlpost CP₂, the resonator R₃ includes therein a control post CP₃, theresonator R₄ includes therein a control post CP₄, and the resonator R₅includes therein a control post CP₅. As in the case of the resonatorR_(x), the control posts CP₁ to CP₅ which do not need to be particularlydiscriminated from each other are each referred to as a control postCP_(x).

Each control post CP_(x) is similar in configuration to the conductorposts constituting the post wall 114. The control post CP_(x) has adiameter of, for example, 100 μm.

Assuming that a shortest distance from the control post CP₁ to a narrowwall of the resonator R₁ is a shortest distance d₁, a shortest distancefrom the control post CP₂ to a narrow wall of the resonator R₂ is ashortest distance d₂, a shortest distance from the control post CP₃ to anarrow wall of the resonator R₃ is a shortest distance d₃, a shortestdistance from the control post CP₄ to a narrow wall of the resonator R₄is a shortest distance d₄, and a shortest distance from the control postCP₅ to a narrow wall of the resonator R₅ is a shortest distance d₅, theshortest distances d₁, d₂ satisfy d₁>d₂, and the shortest distances d₄,d₅ satisfy d₄<d₅. Further, the shortest distance d₃ satisfies d₂>d₃ andd₃<d₄.

Note that the description of the first embodiment discusses the case ofemploying n=5 as the number n of the resonators as illustrated in FIG. 1. When the number n of the resonators is generalized, the filter device1 can be described as including the post-wall waveguide functioning as aresonator group including n resonators R₁, R₂, . . . , R_(n) (n is anodd number not less than five) which are electromagnetically coupledtogether and which are congruent with each other, the resonators R₁, R₂,. . . , R_((n−1)/2) being configured such that (1) the resonator R_(i)(i=1, 2, . . . , (n−1)/2) includes therein a control post CP_(i) and (2)a shortest distance d_(i) from the control post CP_(i) to a narrow wallof the resonator R_(i) satisfies d₁>d₂> . . . >d_((n−1)/2), theresonators R_((n+1)/2+1), R_((n+1)/2+2), . . . , R_(n) being configuredsuch that (1) the resonator R_(j) (j=(n+1)/2+1, (n+1)/2+2, . . . , n)includes therein a control post CP_(j) and (2) a shortest distance d_(j)from the control post CP_(j) to a narrow wall of the resonator R_(j)satisfies d_((n+1)/2+1)<d_((n+1)/2+2)< . . . <d_(n).

Further, in the filter device 1, the resonator R_((n+1)/2) includestherein a control post CP_((n+1)/2), and a shortest distance d_((n+1)/2)from the control post CP_((n+1)/2) to a narrow wall of the resonatorR_((n+1)/2) satisfies d_((n−1)/2)>d_((n+1)/2) andd_((n+1)/2)<d_((n+1)/2+1).

The description of the filter device 1 of the first embodiment discussesthe case where the resonator R₃, which is an example of the resonatorR_((n+1)/2), includes therein the control post CP₃. However, the controlpost CP₃ can be omitted when the respective resonance frequencies of theresonators R₁, R₂, R₄, and R₅ do not need to be adjusted in accordancewith the resonance frequency corresponding to an effective area of theresonator R₃ which is determined on the basis of (i) the area which theresonator R₃ has when it is designed and (ii) the sizes of the couplingwindows A23, A34.

As illustrated in (b) of FIG. 1 , each control post CP_(k) (k=1, 2, . .. , 5) is preferably disposed at a position which does not block thecoupling window for electromagnetically coupling the resonator R_(k) tothe resonator R_(k−1) or the resonator R_(k+1).

Since the resonator R_(x) is cylindrical in the first embodiment, theposition which does not block the coupling window can be described asfollows. Specifically, in a case where, for example, the resonator R₂ isseen in plan view, the position which does not block the couplingwindows A12 and A23 is a position in fan-shaped regions which form apart of the circular resonator R₂ and which are outside fan-shapedregions whose chords are the coupling windows A12 and A23.

[Group of Variations]

(First and Second Variations)

The following description will discuss, with reference to FIG. 2 , apost-wall waveguide 11A and a post-wall waveguide 11B which are a firstvariation and a second variation, respectively, of the post-wallwaveguide 11. (a) of FIG. 2 is a plan view schematically illustratingthe post-wall waveguide 11A. (b) of FIG. 2 is a plan view schematicallyillustrating the post-wall waveguide 11B. Of the components of thepost-wall waveguide 11A, (a) of FIG. 2 does not illustrate thedielectric substrate 111, the first broad wall 112, and the second broadwall 113 but schematically illustrates only a post wall 114A with asolid line. The post wall 114A corresponds to the post wall 114 of thepost-wall waveguide 11. Note that the solid line is obtained byconnecting, by arcs or straight lines, the respective centers of theconductor posts constituting the post wall 114A. Similarly, (b) of FIG.2 schematically illustrates only a post wall 114B with a solid line.

The post-wall waveguide 11A functions as six (n=6) resonators R₁ to R₆,an input waveguide R₈, and an output waveguide R₉. As illustrated in (a)of FIG. 2 , a pattern in which the post wall 114A is disposed isdetermined so that a space bounded by the first broad wall 112, thesecond broad wall 113, and the post wall 114A includes the componentsbelow.

-   -   the input waveguide R₈,    -   a resonator R₁ electromagnetically coupled to the input        waveguide R₈ via a coupling window A81,    -   a resonator R₂ electromagnetically coupled to the resonator R₁        via a coupling window A12,    -   a resonator R₃ electromagnetically coupled to the resonator R₂        via a coupling window A23,    -   a resonator R₄ electromagnetically coupled to the resonator R₃        via a coupling window A34,    -   a resonator R₅ electromagnetically coupled to the resonator R₄        via a coupling window A45,    -   a resonator R₆ electromagnetically coupled to the resonator R₅        via a coupling window A56, and    -   the output waveguide R₉ electromagnetically coupled to the        resonator R₆ via a coupling window A69.

Further, the resonator R₁ includes therein a control post CP₁, theresonator R₂ includes therein a control post CP₂, the resonator R₅includes therein a control post CP₅, and the resonator R₆ includestherein a control post CP₆. In other words, the resonators R₃ and R₄ donot include therein control posts CP₃ and CP₄, respectively.

Assuming that a shortest distance from the control post CP₁ to a narrowwall of the resonator R₁ is a shortest distance d₁, a shortest distancefrom the control post CP₂ to a narrow wall of the resonator R₂ is ashortest distance d₂, a shortest distance from the control post CP₅ to anarrow wall of the resonator R₅ is a shortest distance d₅, and ashortest distance from the control post CP₆ to a narrow wall of theresonator R₆ is a shortest distance d₆, the shortest distances d₁, d₂satisfy d₁>d₂, and the shortest distances d₅, d₆ satisfy d₅<d₆.

Note that the description of the post-wall waveguide 11A discusses thecase of employing n=6 as the number n of the resonators as describedabove. When the number n of the resonators is generalized, the filterdevice 1 including the post-wall waveguide 11A is described as includinga post-wall waveguide functioning as a resonator group including nresonators R₁, R₂, . . . , R_(n) (n is an even number not less than six)which are electromagnetically coupled together and which are congruentwith each other, the resonators R₁, R₂, . . . , R_(n/2−1) beingconfigured such that (1) each resonator R_(i) (i=1, 2, . . . , n/2−1)includes therein a control post CP_(i) and (2) a shortest distance d_(i)from the control post CP₁ to a narrow wall of the resonator R₁ satisfiesd₁>d₂> . . . >d_(n/2−1), the resonators R_(n/2+2), R_(n/2+3), . . . ,R_(n) being configured such that (1) each resonator R_(j) (j=n/2+2,n/2+3, . . . , n) includes therein a control post CP_(j) and (2) ashortest distance d_(j) from the control post CP_(j) to a narrow wall ofthe resonator R_(j) satisfies d_(n/2+2)<d_(n/2+3)< . . . <d_(n).

In addition, the filter device 1 including the post-wall waveguide 11Acan be configured such that the resonators R₃ and R₄ include thereincontrol posts CP₃ and CP₄, respectively. In other words, the filterdevice 1 can be configured such that the resonator R_(n/2) and theresonator R_(n/2+1) include therein a control post CP_(n/2) and acontrol post CP_(n/2+1), respectively, and a shortest distance d_(n/2)from the control post CP_(n/2) to a narrow wall of the resonator R_(n/2)satisfies d_(n/2−1)>d_(n/2) and a shortest distance d_(n/2+1) from thecontrol post CP_(n/2+1) to a narrow wall of the resonator R_(n/2+1)satisfies d_(n/2+1)<d_(n/2+2).

The post-wall waveguide 11B (see (b) of FIG. 2 ), which is based on thepost-wall waveguide 11 illustrated in FIG. 1 , is obtained by addingresonators R₀ and R₆ to the post-wall waveguide 11.

The resonator R₀ is followed by the resonator R₁ and has a smaller areathan the resonator R₁ (and the resonators R₂ to R₅). The resonator R₆follows the resonator R₅ and has a smaller area than the resonator R₅(and the resonators R₁ to R₄). In other words, the resonator R₀ and theresonator R₆ have a radius r₀ and a radius r₆, respectively, each ofwhich is less than a radius r₁ of the resonator R₁ (and the resonatorsR₂ to R₅). Neither the resonator R₀ nor the resonator R₆ includestherein any control post such as the control posts CP₁ to CP₅.

(Third to Fifth Variations)

The following description will discuss, with reference to FIG. 3 , apost-wall waveguide 11C, a post-wall waveguide 11D, and a post-wallwaveguide 11E, which are a third variation, a fourth variation, and afifth variation, respectively, of the post-wall waveguide 11. (a) ofFIG. 3 is a plan view schematically illustrating the post-wall waveguide11C. (b) of FIG. 3 is a plan view schematically illustrating thepost-wall waveguide 11D. (c) of FIG. 3 is a plan view schematicallyillustrating the post-wall waveguide 11E. Of the components of thepost-wall waveguide 11C, (a) of FIG. 3 does not illustrate thedielectric substrate 111, the first broad wall 112, and the second broadwall 113 but schematically illustrates only a post wall 114C with asolid line. The post wall 114C corresponds to the post wall 114 of thepost-wall waveguide 11. Note that this solid line is obtained byconnecting, by arcs or straight lines, the respective centers ofconductor posts constituting the post wall 114C. Similarly, (b) and (c)of FIG. 3 schematically illustrate only a post wall 114D and a post wall114E with a solid line.

The resonators R₁ to R₅ of the post-wall waveguide 11 illustrated inFIG. 1 are each cylindrical. However, as illustrated in (a) to (c) ofFIG. 3 , resonators constituting the post-wall waveguide of a filterdevice in accordance with an aspect of the present invention can havethe shape of a quadrangular prism having rectangular bases, and all ofthe resonators can be linearly disposed.

The post-wall waveguide 11C illustrated in (a) of FIG. 3 functions asfive resonators R₁ to R₅, an input waveguide R₈, and an output waveguideR₉.

The resonator R₁ includes therein a control post CP₁, the resonator R₂includes therein a control post CP₂, the resonator R₄ includes therein acontrol post CP₄, and the resonator R₅ includes therein a control postCP₅. In other words, the resonator R₃ does not include therein a controlpost CP₃.

A shortest distance d₁ from the control post CP₁ to a narrow wall of theresonator R₁ and a shortest distance d₂ from the control post CP₂ to anarrow wall of the resonator R₂ satisfy d₁>d₂. A shortest distance d₄from the control post CP₄ to a narrow wall of the resonator R₄ and ashortest distance d₅ from the control post CP₅ to a narrow wall of theresonator R₅ satisfy d₄<d₅.

Alternatively, in the post-wall waveguide 11C, the resonator R₃ caninclude therein a control post CP₃. In this case, a shortest distance d₃from the control post CP₃ to a narrow wall of the resonator R₃ satisfiesd₂>d₃ and d₃<d₄.

As illustrated in (a) of FIG. 3 , each control post CP_(k) (k=1, 2, 4,5) is preferably disposed at a position which does not block a couplingwindow for electromagnetically coupling the resonator R_(k) to theresonator R_(k−1) or the resonator R_(k+1). This applies to thepost-wall waveguide 11D (described later) and the post-wall waveguide11E (described later).

Since each resonator R_(x) has the shape of a quadrangular prism in thefirst embodiment, the position which does not block the coupling windowcan be described as follows. Specifically, in a case where, for example,the resonator R₂ is seen in plan view, the position which does not blockcoupling windows A12 and A23 is a position outside a trapezoidal regionhaving a pair of bases which are the coupling windows A12 and A23.

The post-wall waveguide 11D illustrated in (b) of FIG. 3 functions assix resonators R₁ to R₆, an input waveguide R₈, and an output waveguideR₉.

The resonator R₁ includes therein a control post CP₁, the resonator R₂includes therein a control post CP₂, the resonator R₃ includes therein acontrol post CP₃, the resonator R₄ includes therein a control post CP₄,the resonator R₅ includes therein a control post CP₅, and the resonatorR₆ includes therein a control post CP₆.

A shortest distance d₁ from the control post CP₁ to a narrow wall of theresonator R₁ and a shortest distance d₂ from the control post CP₂ to anarrow wall of the resonator R₂ satisfy d₁>d₂. A shortest distance d₅from the control post CP₅ to a narrow wall of the resonator R₅ and ashortest distance d₆ from the control post CP₆ to a narrow wall of theresonator R₆ satisfy d₅<d₆.

A shortest distance d₃ from the control post CP₃ to a narrow wall of theresonator R₃ satisfies d₂>d₃ and a shortest distance d₄ from the controlpost CP₄ to a narrow wall of the resonator R₄ satisfies d₄<d₅.

The post-wall waveguide 11E (see (c) of FIG. 3 ), which is based on thepost-wall waveguide 11C illustrated in (a) of FIG. 3 , is obtained byadding resonators R₀ and R₆ to the post-wall waveguide 11C.

The resonator R₀ is followed by the resonator R₁ and has a smaller areathan the resonator R₁ (and the resonators R₂ to R₅). The resonator R₆follows the resonator R₅ and has a smaller area than the resonator R₅(and the resonators R₁ to R₄). Neither the resonator R₀ nor theresonator R₆ includes therein any control post such as the control postsCP₁ to CP₅.

Example

The following description will discuss, with reference to FIG. 4 ,characteristics of an Example of the post-wall waveguide 11 illustratedin FIG. 1 . (a) of FIG. 4 is a graph showing characteristics of Exampleof the post-wall waveguide 11. (b) of FIG. 4 is a graph obtained byenlarging a part of (a) of FIG. 4 .

In the present example, the thickness of the dielectric substrate 111was set to 860 μm, a superconductor having a resistance of zero wasemployed as a material of which the first broad wall 112 and the secondbroad wall 113 are made, the radius r_(x) of each resonator R_(x) wasset to r_(x)=2100 μm, the diameter of the control post CP_(x) was set to100 μm, and the shortest distances d₁, d₂, d₃, d₄, and d₅ were set asfollows: d₁=d₅=825 μm, d₂=d₄=435 μm, and d₃=375 μm.

These design parameters were employed so that the configuration of thepost-wall waveguide 11 would be used to provide a band pass filter thepassband of which has a center frequency (i.e., the resonance frequencyof the resonator R_(x)) of around 28 GHz and is ultra-narrow.

FIG. 4 illustrates the results of simulation of wavelength dependence ofS parameters of the post-wall waveguide 11, which are S(1,1) and S(2,1).In the following description, the wavelength dependence of the Sparameter S(1,1) is referred to as a reflection characteristic, and thewavelength dependence of the S parameter S(2,1) is referred to as atransmission characteristic.

(a) and (b) of FIG. 4 show the following: Given that the post-wallwaveguide 11 of the present example has a passband which is a band inwhich the S parameter S(2,1) exceeds −5 dB, that passband has a centerfrequency of 28.46 GHz and a bandwidth of 0.21 GHz. In other words, thepost-wall waveguide 11 of the present example is found to provide anultra-narrow-band band pass filter which is so favorable as to have afractional bandwidth of 0.7% and a reflection characteristic of not morethan −20 dB.

In order to provide such an ultra-narrow-band band pass filter, it isnecessary to precisely control a coefficient of coupling betweenadjacent resonators. For example, in the case of a post-wall waveguidein which the control posts CP₁, CP₂, CP₃, CP₄, and CP₅ are omitted fromthe respective resonators R₁, R₂, R₃, R₄, and R₅ which constitute thepost-wall waveguide 11, (i) respective areas of the resonators R₁, R₂,R₃, R₄, and R₅ and (ii) respective sizes of the coupling windows A12,A23, A34, and A45 are required to be precisely optimized while (i) and(ii) are mutually dependent. However, such a task is very complicatedand difficult.

In the process for designing the post-wall waveguide 11, (i) therespective areas of the resonators R₁ to R₅ and (ii) the respectivesizes of the coupling windows are not required to be precisely optimizedwhile (i) and (ii) are mutually dependent. It is therefore possible toalso design an ultra-narrow-band band pass filter by a simple designprocess.

Aspects of the present invention can also be expressed as follows:

A filter device of a first aspect of the present invention includes apost-wall waveguide functioning as a resonator group including nresonators R₁, R₂, . . . , R_(n) (n is an odd number not less than five)which are electromagnetically coupled together and which are congruentwith each other. The resonator R₁, R₂, . . . , R_((n−1)/2) areconfigured such that (1) each resonator R_(i) (i=1, 2, . . . , (n−1)/2)includes therein a control post CP_(i) and (2) a shortest distance d_(i)from the control post CP_(i) to a narrow wall of the resonator R_(i)satisfies d₁>d₂> . . . >d_((n−1)/2). The resonators R_((n+1)/2+1),R_((n+1)/2+2), . . . , R_(n) are configured such that (1) each resonatorR_(j) (j=(n+1)/2+1, (n+1)/2+2, . . . , n) includes therein a controlpost CP_(j) and (2) a shortest distance d_(j) from the control postCP_(j) to a narrow wall of the resonator R_(j) satisfiesd_((n+1)/2+1)<d_((n+1)/2+2)< . . . <d_(n).

With the above configuration, it is possible to cause the resonators R₁to R_(n) other than the resonator R_((n+1)/2) to each have an effectivearea closer to an effective area of the resonator R_((n+1)/2) bychanging the shortest distance d_(i) from the control post CP_(i) to thenarrow wall of the resonator R_(i) after determining, on the basis of adesign theory, areas of the n congruent resonators R₁ to R_(n) and sizesof coupling windows each of which is for coupling two adjacent ones ofthe resonators. This eliminates optimizing, in the design process of thefilter device in accordance with the first aspect, (i) the areas of theresonators R₁ to R_(n) and (ii) the respective sizes of the couplingwindows, while (i) and (ii) are mutually dependent, and thus makes itpossible to design the filter device by a simple design process.

In particular, in a case of designing a band pass filter of anultra-narrow band, a conventional filter device requires preciselyoptimizing the respective areas of the resonators R₁ to R_(n) and therespective sizes of the coupling windows, while the areas and the sizesare mutually dependent. In contrast, the filter device in accordancewith the first aspect does not require, in the design process thereof,optimizing (i) the areas of the resonators R₁ to R_(n) and (ii) therespective sizes of the coupling windows, while (i) and (ii) aremutually dependent. It is therefore possible to also design anultra-narrow-band filter device in accordance with the first aspect by asimple design process.

In a second aspect of the present invention, a filter device isconfigured such that, in the first aspect, the resonator R_((n+1)/2)includes therein a control post CP_((n+n)/2), and a shortest distanced_((n+1)/2) from the control post CP_((n+1)/2) to the resonatorR_((n+1)/2) satisfies d_((n−1)/2)>d_((n+1)/2) andd_((n+1)/2)<d_((n+1)/2+1).

With the above configuration, it is possible to change the resonancefrequency of each of the resonators R₁ to R_(n)(i.e., the centerfrequency of the passband of the filter device) without changing, of aplurality of design parameters, the design parameters other than aposition of the control post CP₁, i.e., the areas of the resonators R₁to R_(n) and the respective sizes of the coupling windows. It istherefore possible to design a filter device having desiredcharacteristics by a design process still simpler than conventionaldesign processes.

To solve the above problems, a filter device in accordance with a thirdaspect of the present invention includes a post-wall waveguidefunctioning as a resonator group including n resonators R₁, R₂, . . . ,R_(n) (n is an even number not less than six) which areelectromagnetically coupled together and which are congruent with eachother. The resonator R₁, R₂, . . . , R_(n/2−1) are configured such that(1) each resonator R_(i) (i=1, 2, . . . , n/2−1) includes therein acontrol post CP_(i) and (2) a shortest distance d_(i) from the controlpost CP_(i) to a narrow wall of the resonator R_(i) satisfies d₁>d₂> . .. >d_(n/2−1). The resonator R_(n/2+2), R_(n/2+3), . . . , R_(n) areconfigured such that (1) each resonator R_(j) (j=n/2+2, n/2+3, . . . ,n) includes therein a control post CP_(j) and (2) a shortest distanced_(j) from the control post CP_(j) to a narrow wall of the resonatorR_(j) satisfies d_(n/2+2)<d_(n/2+3)< . . . <d_(n).

With the above configuration, it is possible to cause the resonators R₁to R_(n) other than the resonator R_(n/2) and the resonator R_(n/2+1) tohave an effective area closer to an effective area of the resonatorR_(n/2) and the resonator R_(n/2+1) by changing the shortest distanced_(i) from the control post CP₁ to a narrow wall of the resonator R_(i)after determining, on the basis of a design theory, areas of the ncongruent resonators R₁ to R_(n) and sizes of the coupling windows eachof which is for coupling two adjacent ones of the resonators. Thiseliminates optimizing, in the design process of the filter device inaccordance with the third aspect, (i) the areas of the resonators R₁ toR_(n) and (ii) the respective sizes of the coupling windows, while (i)and (ii) are mutually dependent, and thus makes it possible to designthe filter device by a simple design process.

In a fourth aspect of the present invention, a filter device isconfigured such that, in the third aspect, the resonator R_(n/2) and theresonator R_(n/2+1) include therein a control post CP_(n/2) and acontrol post CP_(n/2+1), respectively. A shortest distance d_(n/2) fromthe control post CP_(n/2) to the resonator R_(n/2) satisfiesd_(n/2−1)>d_(n/2) and a shortest distance d_(n/2+1) from the controlpost CP_(n/2+1) to the resonator R_(n/2+1) satisfiesd_(n/2+2)>d_(n/2+1).

With the above configuration, it is possible to change the resonancefrequency of each of the resonators R₁ to R_(n)(i.e., the centerfrequency of a passband of the filter device) without changing, of theplurality of design parameters, the design parameters other than aposition of the control post CP₁, i.e., without changing the areas ofthe resonators R₁ to R_(n) and the respective sizes of the couplingwindows. It is therefore possible to make a design process for a filterdevice having desired characteristics still simpler than conventionaldesign processes.

In a fifth aspect of the present invention, a filter device isconfigured such that, in any one of the first to fourth aspects, theresonator group further includes: a resonator R₀ which is followed bythe resonator R₁ and which has a smaller area than the resonator R₁; anda resonator R_(n+1) which follows the resonator R_(n) and which has asmaller area than the resonator R_(n).

A filter device in accordance with an aspect of the present inventioncan include the resonator R₀ and the resonator R_(n+1) as in the fifthaspect.

In a sixth aspect of the present invention, a filter device isconfigured such that, in any one of the first to fifth aspects, thecontrol post CP_(k) (k=1, 2, . . . , n) is disposed at a position whichdoes not block a coupling window for electromagnetically coupling theresonator R_(k) to the resonator R_(k−1) or the resonator R_(k+1).

With the above configuration, it is possible to dispose each controlpost CP_(k) in a manner that reduces the influence on electromagneticcoupling between the resonator R_(k) and the resonator R_(k−1) orbetween the resonator R_(k) and the resonator R_(k+1).

In a seventh aspect of the present invention, a filter device isconfigured such that, in any one of the first to sixth aspects, all ofthe resonators constituting the resonator group have a cylindrical shapeor a shape of a prism whose bases have a shape of a regular polygonwhich has at least six vertexes. Of all of the resonators, tworesonators coupled together are disposed in plan view in a manner thatsatisfies D<2r_(a), where r_(a) is a radius of a circumscribed circle ofeach of the two resonators and D is a center-to-center distance betweenthe two resonators.

With the above configuration, when a focus is placed on two resonatorswhich are included in the n resonators R₁ to R_(n) and which are coupledtogether, the circumscribed circle of each of the two resonators issymmetric with respect to a straight line which connects the centers ofthe two circumscribed circles. This enables the filter device inaccordance with the seventh aspect to have increased symmetries in termsof the shape of the filter device and thus enables a reduction in thenumber of design parameters.

In an eighth aspect of the present invention, a filter device isconfigured such that, in the seventh aspect, of all of the resonators, afirst-stage resonator is coupled to an input waveguide, and a last-stageresonator is coupled to an output waveguide, and the first-stageresonator and the last-stage resonator are disposed so as to be adjacentto each other

A post-wall waveguide is often soldered onto a substrate on which adevice such as a high-frequency device is mounted. In a case where amaterial for the populated substrate and a material for a substrateincluded in the post-wall waveguide are different from each other, astress acts on the soldered portion due to the difference in linearexpansion coefficient between the material for the populated substrateand the material for the substrate of the post-wall waveguide. When thestress is large, a crack may occur in the soldered portion.

With the above configuration, it is possible to make smaller a maximumwidth of the post-wall waveguide than with a configuration of n linearlydisposed resonators R₁ to R_(n). For example, a post-wall waveguide inwhich the resonators R₁ to R_(n) are linearly disposed has, in planview, a shape of a rectangle composed of a pair of shorter sides and apair of longer sides. In contrast, according to the filter device inaccordance with the eighth aspect, it is possible to shorten a pair oflonger sides. This makes it possible to reduce, the stress which acts onthe soldered portion in the filter device in accordance with the eighthaspect, as compared to a filter device having linearly disposedresonators R₁ to R_(n), and thus reduce the possibility of a crackoccurring in the soldered portion.

In a ninth aspect of the present invention, a filter device isconfigured such that, in any one of the first to sixth aspects, all ofthe resonators constituting the resonator group are cylindrical and arelinearly disposed.

In a tenth aspect of the present invention, a filter device isconfigured such that, in any one of the first to sixth aspects, all ofthe resonators constituting the resonator group (i) have a shape of aquadrangular prism having rectangular bases and (ii) are linearlydisposed.

The ninth and tenth aspects, which have simple configuration of nresonators R₁ to R_(n), make it possible to design a filter devicehaving desired characteristics by a design process still simpler thanconventional design processes.

[Additional Remark]

The present invention is not limited to the first embodiment describedherein, but can be altered by a skilled person in the art within thescope of the claims. An embodiment derived from a proper combination oftechnical means each disclosed in a different embodiment is alsoencompassed in the technical scope of the present invention.

REFERENCE SIGNS LIST

-   -   1: Filter device    -   11, 11A, 11B, 11C, 11D, 11E: Post-wall waveguide    -   111: Dielectric substrate    -   112: First broad wall    -   113: Second broad wall    -   114: Post wall    -   R₀, R₁, R₂, R₃, R₄, R₅, R₆: Resonator    -   R₈: Input waveguide    -   R₉: Output waveguide    -   A80, A01, A81, A12, A23, A34, A45, A56, A59, A69: Coupling        window    -   CP₁, CP₂, CP₃, CP₄, CP₅, CP₆: Control post

The invention claimed is:
 1. A filter device comprising a post-wallwaveguide functioning as a resonator group including n resonators R₁,R₂, . . . , R_(n) (n is an odd number not less than five) which areelectromagnetically coupled together and which are congruent with eachother, the resonators R₁, R₂, . . . , R_((n−1)/2) being configured suchthat (1) each resonator R_(i) (i=1, 2, . . . , (n−1)/2) includes thereina control post CP_(i) and (2) a shortest distance d_(i) from the controlpost CP_(i) to a narrow wall of the resonator R_(i) satisfies d₁>d₂> . .. >d_((n−1)/2), the resonators R_((n+1)/2+1), R_((n+1)/2+2), . . . ,R_(n) being configured such that (1) each resonator R_(j) (j=(n+1)/2+1,(n+1)/2+2, . . . , n) includes therein a control post CP_(j) and (2) ashortest distance d_(j) from the control post CP_(j) to a narrow wall ofthe resonator R_(j) satisfies d_((n+1)/2+1)<d_((n+1)/2+2)< . . . <d_(n).2. The filter device according to claim 1, wherein the resonatorR_((n+1)/2) includes therein a control post CP_((n+1)/2), and a shortestdistance d_((n+1)/2) from the control post CP_((n+1)/2) to the resonatorR_((n+1)/2) satisfies d_((n−1)/2)>d_((n+1)/2) andd_((n+1)/2)<d_((n+1)/2+1).
 3. The filter device according to claim 1,wherein the resonator group further includes: a resonator R₀ which isfollowed by the resonator R₁ and which has a smaller area than theresonator R₁; and a resonator R_(n+1) which follows the resonator R_(n)and which has a smaller area than the resonator R_(n).
 4. The filterdevice according to claim 1, wherein the control post CP_(k) (k=1, 2, .. . , n) is disposed at a position which does not block a couplingwindow for electromagnetically coupling the resonator R_(k) to theresonator R_(k−1) or the resonator R_(k+1).
 5. The filter deviceaccording to claim 1, wherein all of the resonators constituting theresonator group have a cylindrical shape or a shape of a prism whosebases have a shape of a regular polygon which has at least six vertexes,and of all of the resonators, two resonators coupled together aredisposed in plan view in a manner that satisfies D<2r_(a), where r_(a)is a radius of a circumscribed circle of each of the two resonators, andD is a center-to-center distance between the two resonators.
 6. Thefilter device according to claim 5, wherein of all of the resonators, afirst-stage resonator is coupled to an input waveguide, and a last-stageresonator is coupled to an output waveguide, and the first-stageresonator and the last-stage resonator are disposed so as to be adjacentto each other.
 7. The filter device according to claim 1, wherein all ofthe resonators constituting the resonator group are cylindrical andlinearly disposed.
 8. The filter device according to claim 1, whereinall of the resonators constituting the resonator group (i) have a shapeof a quadrangular prism having rectangular bases and (ii) are linearlydisposed.
 9. A filter device comprising a post-wall waveguidefunctioning as a resonator group including n resonators R₁, R₂, . . . ,R_(n) (n is an even number not less than six) which areelectromagnetically coupled together and which are congruent with eachother, the resonators R₁, R₂, . . . , R_(n/2−1) being configured suchthat (1) each resonator R_(i) (i=1, 2, . . . , n/2−1) includes therein acontrol post CP_(i) and (2) a shortest distance d_(i) from the controlpost CP_(i) to a narrow wall of the resonator R_(i) satisfies d₁>d₂> . .. >d_(n/2−1), the resonators R_(n/2+2), R_(n/2+3), . . . , R_(n) beingconfigured such that (1) each resonator R_(j) (j=n/2+2, n/2+3, . . . ,n) includes therein a control post CP_(j) and (2) a shortest distanced_(j) from the control post CP_(j) to a narrow wall of the resonatorR_(j) satisfies d_(n/2+2)<d_(n/2+3)< . . . <d_(n).
 10. The filter deviceaccording to claim 9, wherein the resonator R_(n/2) and the resonatorR_(n/2+1) include therein a control post CP_(n/2) and a control postCP_(n/2+1), respectively, and a shortest distance d_(n/2) from thecontrol post CP_(n/2) to the resonator R_(n/2) satisfiesd_(n/2−1)>d_(n/2), and a shortest distance d_(n/2+1) from the controlpost CP_(n/2+1) to the resonator R_(n/2+1) satisfiesd_(n/2+2)>d_(n/2+1).
 11. The filter device according to claim 9, whereinthe resonator group further includes: a resonator R₀ which is followedby the resonator R₁ and which has a smaller area than the resonator R₁;and a resonator R_(n+1) which follows the resonator R_(n) and which hasa smaller area than the resonator R_(n).
 12. The filter device accordingto claim 9, wherein the control post CP_(k) (k=1, 2, . . . , n) isdisposed at a position which does not block a coupling window forelectromagnetically coupling the resonator R_(k) to the resonatorR_(k−1) or the resonator R_(k+1).
 13. The filter device according toclaim 9, wherein all of the resonators constituting the resonator grouphave a cylindrical shape or a shape of a prism whose bases have a shapeof a regular polygon which has at least six vertexes, and of all of theresonators, two resonators coupled together are disposed in plan view ina manner that satisfies D<2r_(a), where r_(a) is a radius of acircumscribed circle of each of the two resonators, and D is acenter-to-center distance between the two resonators.
 14. The filterdevice according to claim 9, wherein all of the resonators constitutingthe resonator group are cylindrical and linearly disposed.
 15. Thefilter device according to claim 9, wherein all of the resonatorsconstituting the resonator group (i) have a shape of a quadrangularprism having rectangular bases and (ii) are linearly disposed.